Electrical stimulation therapy may be used for various forms of treatment. For example, stimulation therapy may be provided to address neurological issues such as chronic pain, tremors, and the like. In such an example, an implantable stimulation device is typically located in one location of convenience and is connected to electrical leads that are routed to a stimulation site such as within the brain, within the spinal column, within the pelvic region, or elsewhere. The electrical leads include electrodes that interface with the tissue at the stimulation site to deliver the stimulation signals from the stimulation device.
It may be useful to also sense physiological signals nearby the stimulation site. Such signals may be useful to tailor the stimulation therapy to the particular condition being treated and/or to better understand the response of the tissue nearby the stimulation site to the stimulation signals. Sensing physiological signals may be especially useful where the stimulation therapy may be at least partially controlled based on the physiological signals.
Sensing physiological signals in proximity to the stimulation site can be problematic particularly for neurological stimulation systems. Other signals that may be present within the body nearby the stimulation site may have a voltage that is orders of magnitude greater than the neurological signal to be sensed. For instance, electrical signals produced by the cardiac system can be very problematic considering the heart may be located in close proximity to the neurostimulation device and leads, especially in the case of deep brain stimulation therapy when the device is located in the upper torso.